Recently, with miniaturization of electronic devices, demands for a high-capacity secondary battery are increasing. In particular, a nonaqueous secondary battery having a high energy density and excellent large-current charge/discharge characteristics as compared with a nickel-cadmium battery or a nickel-hydrogen battery is attracting attention.
As for the negative electrode material of a nonaqueous secondary battery, graphite is often used in view of cost, durability and capacity. However, when the active material layer containing a negative electrode material on a polar plate is highly densified so as to obtain a high capacity, there arises a problem that the charge/discharge irreversible capacity in the initial cycle increases, sufficient charge acceptance is not obtained, or cycle deterioration occurs prominently.
Patent Document 1 describes a production method of a carbon composite material, where a natural graphite and a binder are kneaded together to obtain a kneaded material and the kneaded material is subjected to primary heating at 700 to 1,500° C. to carbonize the binder and then to secondary heating at 2,400 to 3,000° C. to thereby simultaneously perform purification of the natural graphite and graphitization of the carbonized binder. However, in Patent Document 1, scaly or flaky natural graphite is envisaged as the starting material, and this is insufficient in terms of highly densifying the active material layer, decreasing the charge/discharge irreversible capacity, or satisfying the charge acceptance and cycle characteristics.